Magnetic coating compositions from carboxylic acid-grafted phenoxy resins

ABSTRACT

Phenoxy resins are acid-grafted by reaction of secondary hydroxyls with monoanhydrides of di- or polycarboxylic acids. The grafted resins have improved adhesion to smooth surfaces, can be readily emulsified, and are also useful in coatings for magnetic recording media.

This application is a division of prior U.S. application Ser. No.725,535, filing date Apr. 22, 1985, now U.S. Pat. No. 4,638,038, issuedJan. 20, 1987.

BACKGROUND OF THE INVENTION

This invention relates to polyhydroxyethers, known as phenoxy resins,and their modification by grafting thereon moieties containing pendantcarboxyl groups.

Phenoxy resins, sometimes referred to herein as "thermoplasticpolyhydroxyethers," are known in the art as components ofcorrosion-resistant coatings, e.g., zinc-rich coatings for metallicsubstrates, as described in U.S. Pat. No. 4,370,382. Phenoxy-basedcoatings of the prior art are not, however, entirely satisfactory inthat their adhesion to smooth substrates, e.g., metallic substrates, issubject to degradation by corrosion, particularly in environments ofhigh humidity.

Carboxylic acids, particularly those with a hydrophobic hydrocarbonchain, are known to have corrosion inhibitive properties for steelexposed to near neutral salt solutions. Salts of weak acids, such asbenzoic acid, have been used as corrosive inhibitors in boiler compoundsand antifreeze solutions. However, organic acids, when used in coatings,often tend to migrate to the steel interface and interfere with theadhesion of the coating resin. It would be very useful, therefore, if away could be found to realize the beneficial corrosion inhibitingeffects of a carboxylic acid-containing coating, but without sufferingthe deleterious effects of the migration of the carboxylic acid.

It is also very desirable if, at the same time, the adhesion of aphenoxy-based coating could be improved, particularly under conditionsof high ambient humidity.

Likewise, it would be desirable to provide compositions which can bereadily emulsified in water, for use where solvent-free or minimumsolvent systems are needed.

The carboxylic acid-containing phenoxy resins of this invention can beused as general purpose and corrosion resistant coatings, andparticularly for highly pigmented systems such as zinc-rich and magneticmedia coatings. These resins have improved dispersing properties forparticulate materials, such as powders. They may be used in adhesivesand laminating systems with improved wet adhesion, and particularly forpolar and metallic substrates. The resins are also useful inwater-dispersible coatings, adhesives and laminating systems.

All these commercially important objectives are met by the presentinvention.

SUMMARY OF THE INVENTION

This invention provides a phenoxy resin having pendant secondaryhydroxyl groups of which about 3 to about 50% of such hydroxyl groupshave been reacted to produce moieties having pendant carboxyl groups.

Also provided is a method for producing such a phenoxy resin,comprising:

(a) preparing a solution of the phenoxy resin, a monoanhydride of a di-or polycarboxylic acid, and a catalytically effective amount of an aminecatalyst, in a nonreactive solvent, and

(b) maintaining the solution at such temperature that reaction proceedsto form a grafted phenoxy resin in which about 3 to about 50%,preferably about 5 to about 25%, of the hydroxyl groups of the phenoxyresin have been reacted with the anhydride to produce moieties havingpendant carboxyl groups.

In addition, this invention comprises a phenoxy coating compositioncomprising:

(a) a phenoxy resin having pendant secondary hydroxyl groups of whichabout 3 to about 50%, preferably about 5 to about 25%, of such hydroxylgroups have been reacted to produce moieties having pendant carboxylgroups, and

(b) a carrier for said phenoxy resin, said coating composition whencoated onto steel, having improved adhesion to the steel under highhumidity conditions as compared to said phenoxy resin not so reacted,and

(c) optionally, a particulate material, such as a pigment, iron oxidepowder, and the like.

This invention further provides an aqueous emulsion comprising:

(a) a phenoxy resin having pendant secondary hydroxyl groups of whichabout 3 to about 50%, preferably about 5 to about 25%, of such hydroxylgroups have been reacted to produce moieties having pendant carboxylgroups, at least some (e.g., about 40 to about 100%, preferably about 60to about 90%) of which carboxyl groups have been neutralized with anaqueous amine or hydroxide, and

(b) water.

Also provided is a method for producing such an emulsion, comprising:

(a) preparing a solution of said phenoxy resin in an organic solvent,

(b) adding said solution, with stirring, to a solution of an alkalineagent in water,

(c) maintaining the resulting mixture at a temperature and for a timesufficient to effect a reaction whereby a sufficient number (e.g., about40 to about 100%, preferably about 60 to about 90%) of carboxyl groupsare neutralized to provide a stable emulsion,

(d) volatilizing the solvent to produce a stable, essentiallysolvent-free or low solvent emulsion.

In addition, this invention provides a magnetic coating composition formagnetic recording media comprising:

(a) a phenoxy resin having pendant secondary hydroxyl groups of whichabout 3 to about 50%, preferably about 5 to about 25%, of such hydroxylgroups have been reacted to produce moieties having pendant carboxylgroups,

(b) a magnetic powder, and

(c) an organic solvent,

and wherein the magnetic powder is present in the concentration range ofabout 1:1 to about 30:1 preferably about 1.5:1 to about 10:1 magneticpowder:phenoxy resin.

Finally, this invention provides an article comprising a substratecoated with the above coating compositions or emulsions.

DETAILED DESCRIPTION OF THE INVENTION

The carboxylic acid-grafted phenoxy resins of this invention areachieved by reaction of monoanhydrides of di- or polycarboxylic acidswith a certain proportion, preferably about 5 to about 25%, of thesecondary hydroxyl groups present on the resin's polymeric chain. Ingeneral, the polymer should have a molecular weight of about 15,00 toabout 45,000, preferably about 22,000 to about 37,000 and ideally about30,000. It is imperative that a monoester be formed and that diesterformation be as close to nil as possible, since diester formation willresult in a high viscosity or gel. The monoester reaction willpredominate at controlled reaction temperatures and under the influenceof catalysis, generally of the tertiary amine type. In addition, thephenoxy resin should contain little or no epoxide functionality, therebyavoiding any possible reaction with the carboxyl groups.

The terms "thermoplastic poly(hydroxyether)" and "phenoxy" herein referto substantially linear polymers having the general formula:

    [--D--O--E--O--].sub.n

wherein D is the radical residuum of a dihydric phenol, E is anhydroxyl-containing radical residuum of an epoxide and n represents thedegree of polymerization and is at least 30 and is preferably 80 ormore. The term "thermoplastic poly(hydroxyether)" is intended to includemixtures of at least two thermoplastic poly(hydroxyethers).

The thermoplastic poly(hydroxyethers) can be prepared by admixing fromabout 0.985 to about 1.015 moles of an epihalohydrin with one mole of adihydric phenol together with from about 0.6 to 1.5 moles of an alkalimetal hydroxide, such as, sodium hydroxide or potassium hydroxide,generally in an aqueous medium, at a temperature of about 10° to about50° C. until at least about 60 mole percent of the epihalohydrin hasbeen consumed. The thermoplastic poly(hydroxyethers) thus produced havereduced viscosities of at least about 0.4. Reduced viscosity values arecomputed by use of the equation: ##EQU1## wherein t_(o) is the effluxtime of the solvent (tetrahydrofuran), t_(s) is the efflux time of thepoly(hydroxyether) solution, c is the concentration of thepoly(hydroxyether) solution in grams of poly(hydroxyether) per 100 ml.of tetrahydrofuran.

The dihydric phenol contributing the phenol radical residuum, D, can beeither a dihydric mononuclear or a dihydric polynuclear phenol such asthose having the general formula: ##STR1## wherein Ar is an aromaticdivalent hydrocarbon such as naphthylene and, preferably, phenylene, Yand Y₁ which can be the same or different are alkyl radicals, preferablyhaving from 1 to 4 carbon atoms, halogen atoms, i.e., fluorine,chlorine, bromine and iodine, or alkoxy radicals, preferably having from1 to 4 carbon atoms, r and z are integers having a value from 0 to amaximum value corresponding to the number of hydrogen atoms on thearomatic radical (Ar) which can be replaced by substituents and R¹ is abond between adjacent carbon atoms as in dihydroxydiphenyl or is adivalent radical including, for example, ##STR2## --O--, --S--, --SO--,--SO₂ --, and --S--S--, and divalent hydrocarbon radicals such asalkylene, alkylidene, cycloaliphatic, e.g., cycloalkylidene, halogenatedalkoxy or aryloxy substituted alkylene, alkylidene and cycloaliphaticradicals as well as alkarylene and aromatic radicals includinghalogenated, alkyl, alkoxy or aryloxy substituted aromatic radicals anda ring fused to an Ar group; or R¹ can be polyalkoxy, or polysiloxy, ortwo or more alkylidene radicals separated by a aromatic ring, a tertiaryamino group, an ether linkage, a carbonyl group or a sulfur-containinggroup such as sulfoxide, and the like.

Examples of specific dihydric polynuclear phenols include, among others:

The bis(hydroxyphenyl)alkanes such as

2,2-bis-(4-hydroxyphenyl)propane,

2,4'-dihydroxydiphenylmethane,

bis(2-hydroxyphenyl)methane,

bis(4-hydroxyphenyl)methane,

bis(4-hydroxy-2,6-dimethyl-3-methoxyphenyl)methane,

1,1-bis(4-hydroxyphenyl ethane,

1,2-bis(4-hydroxyphenyl)-ethane,

1,1-bis(4-hydroxy-2-chlorophenyl)ethane,

1,1-bis-(3-methyl-4-hydroxyphenyl)ethane,

1,3-bis(3-methyl-4-hydroxyphenyl)propane,

2,2-bis(3-phenyl-4-hydroxyphenyl)-propane,

2,2-bis(3-isopropyl-4-hydroxyphenyl)propane,

2,2-bis(2-isopropyl-4-hydroxyphenyl)propane,

2,2-bis-(4-hydroxylnaphthyl)propane,

2,2-bis(4-hydroxyphenyl)-pentane,

3,3-bis(4-hydroxyphenyl)pentane,

2,2-bis(4-hydroxyphenyl)heptane,

bis(4-hydroxyphenyl)phenylmethane,

bis(4-hydroxyphenyl)cyclohexylmethane,

1,2-bis(4-hydroxy-phenyl-1,2-bis(phenyl)propane,

2,2,-bis(4-hydroxyphenyl)-1-phenyl-propane and the like;

Di(hydroxyphenyl)sulfones such as

bis(4-hydroxy-phenyl)sulfone, 2,4'-dihydroxyldiphenyl sulfone,5'-chloro-2,4'-dihydroxydiphenyl sulfone,5'-chloro-4,4'-dihydroxydiphenyl sulfone and the like:

Di(hydroxyphenol)ethers such as

bis(4-hydroxy-phenyl)ether, the 4,3'-, 4,2'-, 2,2'-, 2,3'-,di-hydroxydiphenyl ethers,

4,4'-dihydroxy-2,6-dimethyldiphenyl ether,

bis(4-hydroxy-3-isobutylphenyl)ether,

bis(4-hydroxy-3-isopropylphenyl)ether,

bis(4-hydroxy-3-chlorophenyl)-ether,

bis(4-hydroxy-3flurophenyl)ether,

bis(4-hydroxy-3-bromophenyl)ether,

bis(4-hydroxynaphthyl)ether,

bis(4-hydroxy-3-chloronaphthylether,

bis(2-hydroxydiphenyl)-ether,

4,4'-dihydroxy-2,6-dimethoxydiphenyl ether,

4,4-dihydroxy-2,5-diethoxydiphenyl ether, and the like.

Also suitable are the bisphenol reaction products of 4-vinylcyclohexeneand phenols, e.g., 1,3-bis(p-hydroxyphenyl)-1-ethylcyclohexane and thebis-phenol reaction products of dipentene or its isomers and phenolssuch as 1,2-bis(p-hydroxyphenyl)-1-methyl-4-isopropylcyclohexane as wellas bisphenols such as1,3,3'trimethyl-1-(4-hydroxyphenyl)-6-hydroxyindane, and2,4-bis(4-hydroxyphenyl)-4-methylpentane, and the like.

Particularly desirable dihydric polynuclear phenols have the formula##STR3## wherein Y and Y₁ are as previously defined, r and z have valuesfrom 0 to 4, inclusive, and R¹ is a divalent, saturated aliphatichydrocarbon radical, particularly alkylene and alkylidene radicals,having from 1 to 3 carbon atoms, and cycloalkylene radicals having up toand including 10 carbon atoms.

Mixtures of dihydric phenols can also be employed and whenever the term"dihydric phenol" or "dihydric polynuclear phenol" is used herein,mixtures of these compounds are intended to be included.

The epoxide contributing the hydroxyl containing radical residuum, E,can be monoepoxide or diepoxide. By "epoxide" is meant a compoundcontaining an oxirane group, i.e., oxygen bonded to two vicinalaliphatic carbon atoms, thus, ##STR4## A monoepoxide contains one suchoxirane group and provides a radical residuum E containing a singlehydroxyl group, a diepoxide contains two such oxirane groups andprovides a radical residuum E containing two hydroxyl groups. Saturatedepoxides, by which term is meant diepoxides free of ethylenicunsaturation, i.e., >C═C< and acetylenic unsaturation, i.e.,--C.tbd.C--, are preferred. Particularly preferred are halogensubstituted saturated monoepoxides, i.e., the epihalohydrins andsaturated diepoxides which contain solely carbon, hydrogen and oxygen,especially those wherein the vicinal or adjacent carbon atoms form apart of an aliphatic hydrocarbon chain. Oxygen in such diepoxides canbe, in addition to oxirane oxygen, ether oxygen --O--, oxacarbonyloxygen ##STR5## and the like.

Specific examples of monoepoxides include epichlorohydrins such asepichlorohydrin, epibromohydrin, 1,2-epoxy-1-methyl-3-chloropropane,1,2-epoxy-1-butyl-3-chloropropane, 1,2-epoxy-2-methyl-3-fluoropropane,and the like.

Illustrative diepoxides include diethylene glycolbis(3,4-epoxycyclohexane-carboxylate),

bis(3,4-epoxycyclohexyl-methyl)adipate,

bis(3,4-epoxycyclohexyl-methyl)phthalate,

6-methyl-3,4-epoxycyclohexylmethyl-6-methyl-3,4-epoxycyclohexanecarboxylate,

2-chloro-3,4-epoxycylohexylmethyl-2-chloro-3,4-epoxycyclohexane-carboxylate,diglycidyl ether,

bis(2,3-epoxycyclopentyl)-ether, 1,5-pentanediolbis(4-methyl-3,4-epoxycyclohexyl-methyl)ether,

bis(2,3-epoxy-2-ethylhexyl)adipate, diglycidyl maleate, diglycidylphthalate,

3-oxa-tetracyclo[4.4.0.1⁷,10.O²,4 ]-undec-8-yl 2,3-epoxy-propyl ether,

bis(2,3-epoxycyclopentyl)sulfone,

bis(3,4-epoxyhexoxypropyl)sulfone,

2,2'-sulfonyldiethyl,

bis(2,3-epoxycyclopentanecarboxylate),3-oxatetracyclo-[4.4.0.1⁷,10.O.sup.2,4]-undec-8-yl 2,3-epoxybutyrate,

4-pentenal-di-(6-methyl-3,4-epoxycyclohexylmethyl)acetal, ethyleneglycol bis(9,10-epoxystearate), diglycidyl carbonate,

bis(2,3-epoxybutylphenyl)-2-ethylhexyl phosphate,

diepoxydioxane, butadiene dioxide, and 2,3-dimethyl butadiene dioxide.The preferred diepoxides are those wherein each of the oxirane groups isconnected to an electron donating substituent which is not immediatelyconnected to the carbon atoms of that oxirane group. Such diepoxideshave the grouping ##STR6## wherein A is an electron donating substituentsuch as ##STR7## and Q is a saturated hydrocarbon radical such as analkyl, cycloalkyl, aryl or aralkyl radical.

The preferred polyhydroxyether is available commercially as UCAR PhenoxyPKHH, a trade designation of Union Carbide Corporation for acondensation polymer derived from bisphenol-A(2,2-bis(p-hydroxyphenyl)propane and epichlorohydrin having thestructural formula: ##STR8##

The phenoxy resin is available as a solution in glycol ether esters suchas Cellosolve acetate (the acetate of a monoalkyl glycol ether soldunder the Trademark Cellosolve by Union Carbide Corporation) or inpellet form which is readily soluble in a variety of solvents andsolvent blends. The solid phenoxy resin sold under the designation PKHHby Union Carbide Corporation is soluble in the following solvents: butylCarbitol, butyl Carbitol acetate, butyl Cellosolve, Carbitol solvent,Cellosolve acetate, Cellosolve solvent, diacetone alcohol, diethylCarbitol, dimethylformamide, dimethyl sulfoxide, dioxane, ethoxytriglycol, mesityl oxide, methyl Cellosolve acetate, methyl ethylketone, and tetrahydrofuran.

Carbitol is a Trademark of Union Carbide Corporation for the monoalkylether of diethylene glycol.

The preparation of the above-described polyhydroxyethers is described inU.S. Pat. No. 3,305,528.

In addition to these polyhydroxyethers one may also employ the linearthermoplastic polyethers described in U.S. Pat. No. 3,177,089, U.S. Pat.No. 3,306,872, and U.S. Pat. No. 2,602,075.

Typical of the useful anhydrides are: succinic anhydride, citraconicanhydride, itaconic anhydride, alkenyl succinic anhydride, dodecenylsuccinic anhydride, maleic anhydride, dichloromaleic anhydride,chlorendic anhydride, linoleic acid adduct of maleic anhydride,hexahydrophthalic anhydride, methyl tetrahydrophthalic anhydride,tetrahydrophthalic anhydride, maleic anhydride, maleic anhydride adductof methylcyclopentadiene, trimellitic anhydride, phthalic anhydride,nadic anhydride, and the like. Itaconic anhydride, maleic anhydride,tetrahydrophathalic anhydride, linoleic acid adduct of maleic anhydride,and the maleic anhydride adduct of methylcyclopentadiene, all havingreactive double bonds capable of under going polymerization orcopolymerization with other reactive, double bond-containing materialswhen subject to heat, catalysis or radiation, produce coatings withimproved solvent and temperture resistance. Of these, succinic anhydrideand trimellitic anhydride are especially preferred. Trimelliticanhydride has the following structure: ##STR9## Therefore, compared tosuccinic anhydride or other monoanhydrides, each ester graft with thephenoxy resins generates two pendant carboxylic acid groups rather thanone. It allows one to make a more polar molecule and the aromatic esterlinkage is less subject to hydrolysis than that of aliphatic esters.

Suitable catalysts are Lewis bases or electron donors. An importantclass is tertiary amines. Examples of tertiary amines which may be usedto catalyze the reaction of anhydrides with the secondary hydroxyl of apolyhydroxy ether to form a half-ester acid are as follows: lineardiamines, of the formula (CH₃)₂ N(CH₂)_(n) N(CH₃)₂ where n=1 to about 4,N,N,N',--N'-tetramethyl-1,3-butanediamine, alkyl tertiary monoamines, ofthe formula N[(CH₂)_(n) CH₃ ]₃ where n=1 to about 4, e.g.,triethylamine, N,N'-dimethylpiperazine, N-methylmorpholine,triethylenediamine, hexamethylenetetramine, pyridine, pyrazine,quionoline, benzyldimethylamine, alpha-methylbenzyldimethylamine,N-alkyl imidazoles wherein the alkyl group contains 1 to about 4 carbonatoms, N-alkyl imidazolines wherein the alkyl group contains 1 to about4 carbon atoms. Similarly, suitable catalysts include tertiaryphosphines, such as triphenyl phosphine, tricyclohexyl phosphine, andthe like. Of these, triethylene diamine (also known as "Dabco," a tradedesignation of Air Products Company) is especially preferred. Because ofits structure, it is less hindered and more nucleophilic than most othergenerally available amines, and therefore is more effective.

Tertiary amines have an unshared pair of electrons in their outerorbital. They are attracted to areas of reduced electron density in themolecules with which they react. It is postulated (without intending tobe bound to any particular theory) that an activated complex is formed,as shown with the following reaction of Dabco with succinic anhydride:##STR10## which is a quasi 6 membered zwitterion wherein complexationlowers the activation energy of the reaction ##STR11##

PENDANT CARBOXYLIC ACID HALF ESTER

The reaction between the phenoxy and the anhydride is preferablyeffected in a non-reactive solvent, such as dimethyl Carbitol(2-methoxyethylether), 2-ethoxyethyl ether, tetrahydrofuran, 1,4dioxane, ethylene glycol dimethyl ether, ethylene glycol diethyl ether,methylisobutyl ketone, methylethyl ketone, cyclohexanone, dimethylsulfoxide, dimethyl formamide, toluene, and the like. Of these,tetrahydrofuran is particularly preferred. In selecting a solvent, it isimportant to note that the solvent should not contain any reactivehydroxyl groups of hydrolyzable ester linkages.

Alternatively, the phenoxy can be dispersed in a poor solvent, such asan alkylated aromatic, to a fine particle size. The anhydride should besoluble in the solvent to form a continuous phase which can react on thesurface of the particle. An example would be methyltetrahydrophthalicanhydride using benzyldimethylamine as catalyst. The preparation of anonaqueous dispersion of 30,000 molecular weight polyhydroxyether,because of its high melt viscosity, would require a high shear mixer andthe use of a high-boiling solvent or a pressue vessel to preventevaporation of the solvent.

The desired reaction is illustrated by the reaction between Phenoxy PKHHand succinic anhydride: ##STR12##

The concentrations of the various materials may vary substantially,depending upon the materials and operating condidtions selected.Optimization of the reaction would be a matter of routineexperimentation within the skill of the art. In general, however, it maybe expected that, on a weight percent basis, the concentration of thephenoxy resin would be about 98.9 to about 74.8, preferably about 97 toabout 88%; the concentration of the anhydride would be about 1 to about25, preferably about 3 to about 12%; and the concentration of thecatalyst would be about 0.05 to about 0.5%.

The reaction mixture should be well stirred, and the reaction should becarried out at a temperature of about 80° to about 145°, preferablyabout 115° to about 135° C. These temperature ranges are recommended toobtain reasonable reaction rates without incurring gel problems. Whentemperatures as high as 145° C. are used, viscosity increase willprobably be noted, indicating some reaction between the carboxyl andhydroxyl groups.

In conducting the reaction, it is desirable that only a minority of theavailable secondary hydroxyl groups be converted, in order to permit alater hydroxyl cross-linking reaction and to minimize water sensitivityof the polymer. Typically, only about 3 to about 50, preferably about 5to about 25% of the available hydroxyls are reacted. Sufficient hydroxylgroups should be left in the phenoxy so the combination of hydroxyl andcarboxy groups can co-react or react with cross-linkers, such as avariety of di- or polyisocyanates or melamine formaldehyde. The percentconversion is controlled by selecting the number of mols of anhydridenecessary to react with the hydroxyl groups on the phenoxy, and thencarrying out the reaction until no anhydride groups remain. Whenunsaturated anhydrides, such as tetrahydrophthalic anhydride, are used,additional cross-linking can take place via polymerization orcopolymerization with other unsaturated materials by using heat,catalysis or radiation.

The invention is illustrated in more detail in the following examples.All parts and percentages are by weight, based on the entire recipe.

EXAMPLE 1 Preparation of Succinic Anhydride-Grafted Phenoxy Resin

1. 175 grams of dimethyl "Carbitol" were charged to a 500 cc flask. Withgood agitation, 83 grams dried (16 hours at 90° C.) Phenoxy PKHH resinwere added.

2. The flask was heated to 150°-160° C. to dissolve the resin. 25 gramsof the solvent were distilled off in order to drive off moisture in theresin solution which could react with the anhydride and result in somedicarboxylic acid formation.

3. The temperature was reduced to 120°-125° C. and 5.85 grams ofsuccinic anhydride and 0.16 gram of triethylenediamine were added inorder to insert one carboxyl group per 5 repeating units of phenoxy. Thetemperature was held at 120°-125° C. for the duration of the reaction.

4. The product was sampled periodically over 60 minutes, and it wasdetermined by Fourier Transform Infrared Spectroscopy that the reactionhad been completed in 5 minutes.

5. 86 grams of dimethyl "Carbitol" were then added to reduce the solidsto 25%, and the flask was cooled to room temperature.

The viscosity of the succinic acid-grafted phenoxy at the 25% solidscontent was identical to that of the Phenoxy PKHH resin solution (9strokes at 20° C.), indicating that the primary reaction was half-estercarboxylic acid formation with little or no diester formarion.

EXAMPLE 2

The procedure of Example 1 was repeated, except that tetrahydrofuran(THF) was used as the solvent instead of dimethyl Carbitol. The THF wasdried over molecular sieves. Because of the relatively low boiling pointof THF, the reaction was run at 64° C., which of course caused anincrease in reaction time. The reaction again was tracked by takingperiodic samples and analyzing them by Fourier Transform Infra-redSpectroscopy. The results are shown in Table I. In this table, the"Carbonyl Ratio" column shows the ratio of carbonyl peak heights ofbands assigned to anhydride and esters. It is apparent from these datathat the reaction was virtually over within 3 hours when triethylenediamine is used as a catalyst. The reaction is much closer to completionin 10 minutes with the catalyst than after 51/2 hours without acatalyst.

                  TABLE I                                                         ______________________________________                                        REACTION RATE OF SUCCINIC                                                     ANHYDRIDE WITH PHENOXY RESIN IN THF                                                      Carbonyl Ratio                                                     Reaction Time                                                                              No Catalyst                                                                              Triethylenediamine                                    ______________________________________                                        10 mins.     6.0        0.67                                                  1 hr.        6.87       0.16                                                  3 hrs.       3.29       0.008                                                 51/2 hrs.    2.57       0.00                                                  ______________________________________                                    

EXAMPLE 3

The procedure of Example 1 was repeated, except that benzyldimethylaminewas used as the catalyst instead of triethylenediamine. Again asatisfactory acid-grafted phenoxy resin was obtained.

EXAMPLE 4 Preparation of Trimellitic Anhydride-Grafted Phenoxy Resin

1. 170.4 grams of dried Phenoxy PKHH were dissolved in 300 grams of dryTHF and the solution was charged to a 1-liter, 4-neck flask equippedwith a stirrer and reflux condenser.

2. 23.1 grams of trimellitic anhydride and 0.3 gram oftriethylenediamine (Dabco) were introduced with stirring.

3. The temperature was raised to 60° C. and the mixture was maintainedovernight at that temperature.

4. 267 grams of THF were added, and the temperature was brought toambient temperature.

The conversion was determined to be 96.5%. Because of the relatively lowvapor pressure of trimellitic anhydride, the reaction was measured usingdifferential titration with alcoholic and aqueous alkali:

It has been found that the anhydride-grafted phenoxy resins of thisinvention can be easily made into excellent emulsions in water. Incontrast, ungrafted phenoxy resins of the prior art, when emulsificationis attempted, do not emulsify but coagulate. Example 5 presents atypical procedure for emulsification.

EXAMPLE 5 Emulsion of Succinic Acid Anhydride-Grafted Phenoxy Resin

One hundred grams of a 25% solution of succinic anhydride-graftedphenoxy in tetrahydrofuran or 2-methoxyethyl ether, heated to 60° C.,were added to the following mixture with stirring: one hundred grams ofa mixture of distilled water 78.72%, butyl Cellosolve 20.01%, anddimethylethanolamine 1.27%, heated to 60° C.

A low viscosity, translucent emulsion was obtained with a pH of 6.9.Dimethylethanolamine, indicated above, was present in the water phase insufficient concentration to form a soap with about 85% of the availablecarboxyl groups.

The tetrahydrofuran was removed in a rotating flask (Roto-Vac) under avacuum of 27 inches of Hg using a 50° C. hot water bath. This thenresults in a solvent-free system.

The emulsion so produced was film-forming at room temperature in thepresence of a small amount of filming agent, such as butyl Cellosolve. Afine powder film is obtained in the absence of a filming agent. Elevatedtemperature would then be required to flux the polymer particles.

Similar excellent results were obtained when a trimelliticanhydride-grafted phenoxy was used in the emulsion instead of thesuccinic anhydride product.

EXAMPLE 6

The procedure of Example 5 was repeated, except that the butylCellosolve cosolvent was deleted from the mixture. Again, excellenttranslucent micro-emulsions were obtained. In this case, however, theemulsions were not film-forming at room temperature; instead, theyproduced a fine powdery, non-adhering coating.

EXAMPLE 7 Emulsion Stability

Phenoxy emulsions prepared by either succinic anhydride or trimelliticanhydride grafting were observed for stability at ambient temperature.Table II demonstrates that emulsion stability was good.

                  TABLE II                                                        ______________________________________                                        STABILITY OF WATER DISPERSION.sup.1                                           %.sup.2    Solvent          Storage.sup.3                                     ______________________________________                                        Succinic Anhydride                                                             5%        10% Bu Cellosolve                                                                              >6 months                                         10%        10% Bu Cellosolve                                                                              >6 months                                         20%        10% Bu Cellosolve                                                                              4 months                                          20%        None             4 months                                          Trimellitic Anhydride                                                          5%        None             >6 months                                         10%        None             >6 months                                         20%        None             3 months                                          ______________________________________                                         .sup.1 Dimethylethanolamine neutralized  85%                                  .sup.2 Percent stoichiometry                                                  .sup.3 Storage time at ambient temperature for which emulsion remains         stable                                                                   

EXAMPLE 8 Physical Properties of Acid-Grafted Phenoxy Resins

Succinic anhydride-grafted Phenoxy PKHH was prepared using sufficientsuccinic anhydride to react with varying percentages of the availablehydroxyl groups in the molecule (percent stoichiometry). The reactionswere carried out in tetrahydrofuran and the resulting resins wereprecipitated in isopropanol to produce a powder which was recovered formolding. 25 mil sheets were compression molded at 150° C. and tested forphysical properties, shown in Table III. Particular attention should begiven to the elongation at break, and pendulum impact, which are ameasures of toughness. It is observed that the phenoxy can be grafted upto about 20-40% of its hydroxyl stoichiometry without degrading itsphysical properties below the level of commercial acceptability.

The physical properties of trimellitic anhydride, phthalic anhydride andtetrahydrophthalic anhydride grafts are shown in Table IV. In this case,the number of carboxylic acid groups generated by grafting is two timesthe number of hydroxyls involved in the reaction. The aromatic nature ofthe trimellitic anhydride stiffens the backbone of the phenoxy more thanthe pendant aliphatic anhydride. Table IV shows that the toughnessproperties are retained between 5 and 10% stoichiometry.

Phthalic anhydride and tetrahydrophthalic anhydride were grafted at 20%stoichiometry only.

                  TABLE III                                                       ______________________________________                                        PHYSICAL PROPERTIES (AVERAGE) OF ACID-                                        GRAFTED PHENOXY RESINS SUCCINIC ANHYDRIDE                                                                      Elong.                                                Tensile  Tensile  Yield at    Pend.                                  Stoichiometry                                                                          Strength Modulus  Elong.                                                                              Break Impact                                 %        (1000 psi)                                                                             (1000 psi)                                                                             %     %     ft-lbs/in.sup.3                        ______________________________________                                        Control 0                                                                              7.7      251      4.8   82    146                                     5       8.7      260      6.2   111   108                                    10       7.5      250      4.7   44    140                                    20       8.9      271      5.7   36     93                                    40       9.4      287      5.2   43     89                                    90       8.4      295      4.5   32     18                                    ______________________________________                                    

                  TABLE IV                                                        ______________________________________                                        PHYSICAL PROPERTIES (AVERAGE) OF ACID-                                        GRAFTED PHENOXY RESINS                                                                                          Elong.                                                Tensile  Tensile  Yield at    Pend.                                 Stoichiometry                                                                           Strength Modulus  Elong.                                                                              Break Impact                                %         (1000 psi)                                                                             (1000 psi)                                                                             %     %     ft-lbs/in.sup.3                       ______________________________________                                        Trimellitic Anhydride                                                          0        7.7      251      4.8   82    146                                    21/2     6.3      207      5.2   90    141                                    5        6.5      214      5.3   75    108                                   10        6.9      224      5.0   58    84                                    20        7.7      222      6.0   13    17                                    40        8.6      261      5.5   10    11                                    Phthalic Anhydride                                                            20        6.2      208      5.3   28    26                                    Tetrahydrophthalic Anhydride                                                  20        6.4      210      5.3   34    94                                    ______________________________________                                    

EXAMPLE 9 Coatings Properties

Succinic anhydride and trimellitic anhydride-grafted phenoxy resins wereapplied as coatings to cold-rolled steel using the following procedure:Cold-rolled steel panels (Q-steel) were cleaned with methyl ethyl ketoneand dried in an oven at 60° C. A coating was applied using a wet filmapplicator having a 3-mil gap. The coating was dried for 1 hour at 25°C. A second coat was applied on top of the first, and was driedsimilarly. The panels were then baked for 20 minutes at 100° C. Theresulting panels had a dry film thickness of 0.9 mil and were exposed tohigh humidity conditions and salt spray to test their resistance tocorrosion. Testing was performed using ASTM D-2247 in a ClevelandHumidity apparatus Model No. QCT-MDO, manufactured by Q-Panel Co. ofCleveland, Ohio. Exposure conditions were 500 hours at 120° F. (49° C.).Results are reported in Table V.

                  TABLE V                                                         ______________________________________                                        GRAFT-PHENOXY COATINGS ON COLD-                                               ROLLED STEEL                                                                  Exposure Conditions:                                                          Cleveland Humidity - 120° F./500 hours                                             Corrosion                                                                              Cross Hatch Adhesion                                     ______________________________________                                        Succinic Acid (20%)                                                                         8          100%                                                 Grafted Phenoxy PKHH                                                          Phenoxy PKHH  4          0                                                    Salt Spray - 750 hours                                                        Succinic Acid-                                                                              7                                                               Grafted Phenoxy PKHH                                                          Phenoxy PKHH  7                                                               ______________________________________                                    

Table V shows that the succinic anhydride-grafted phenoxy retains goodcross-hatch adhesion after 500 hours of Cleveland Humidity at 120° F.Ungrafted Phenoxy PKHH shows complete loss of adhesion under the sameconditions. There is also an advantage in corrosion resistance shown bythe grafted phenoxy (a corrosion rating of 10 indicates no change,whereas a rating of 0 is complete failure). Salt spray resistance wasevaluated using ASTM B-117. Cross-hatch adhesion was tested using ASTMD-3359-83 (Method B), with the variation that rating was based on thepercent of squares not removed, i.e., all removed--0% adhesion, nonremoved--100% adhesion.

Curiously, salt spray test results did not show an improvement for thegrafted resin over the ungrafted.

EXAMPLE 10 Coatings Properties

Trimellitic anhydride-grafted phenoxy resins were applied and tested ina similar manner. Table VI shows the results of Cleveland HumidityTests. Significant adhesion degradation is seen for resins acid-graftedwith less than 5% of the hydroxyl stoichiometry. It was noted that theresins in the 20-40% graft range retained good adhesion in spite of thefact that they were white from water blush.

                  TABLE VI                                                        ______________________________________                                        TRIMELLITIC ANHYDRIDE-GRAFTED PHENOXY                                         COATINGS ON COLD-ROLLED STEEL                                                 Exposure: Cleveland Humidity - 120° F./250 Hours                       Stoichiometry (%)                                                                         Corrosion  Cross-Hatch Adhesion                                   ______________________________________                                        0 - Phenoxy PKHH                                                                          3          0%                                                     21/2        5          0%                                                     5           7          100%                                                   10          7          100%                                                   20          --         100%     (Blush)                                       40          --         100%     (Heavy Blush)                                 ______________________________________                                    

Similarly to the results for salt spray of the succinicanhydride-grafted phenoxy resins, the trimellitic anhydride-graftedresins show no significant improvement in salt spray performance.

From the practical standpoint, however, most coatings do not see saltspray conditions, but rather, high humidity which results in loss ofadhesion and failure of the paint. Retention of adhesion under fieldconditions, which are better reflected by the non-salt test, shouldprovide improved coating longevity.

It may also be desirable in some cases that the acid-grafted phenoxyresins be used in coatings with a small amount of epoxy resin so thatany carboxyl groups which cannot orient themselves to the steel, due tothe rigidity of the polymer backbone, will be tied up and therefore notcontribute to water sensitivity. Statistically, not all the carboxylgroups can interact with the surface.

A very useful and surprising advantage of the grafted phenoxy resins ofthis invention is their beneficial reduction of the viscosity ofiron-oxide-containing formulations. This effect should permit theformulation of higher solids iron oxide coatings, which should be usefulin, e.g., the manufacture of magnetic media. This effect is illustratedin the following example:

EXAMPLE 11 Effect of Carboxylic Acid Grafted-Phenoxy on Rheology

Table VII shows the effect of trimellitic anhydride acid grafting on therheology of iron oxide systems. The dispersions were made using a CowlesDissolver, model no. 1 V G, manufactured by Cowles Dissolver Co., ofCayoga, N.Y. The Dissolver was operated at 4,000 rpm. Substitution ofthe acid-grafted phenoxy for conventional resin lowered the 20 rpmviscosity to 50% and the 2 rpm viscosity to 30% of the control. Theviscosity ratio was also reduced. This therefore offers the advantage ofbeing able to apply higher solids coatings at given viscosities.

                  TABLE VII                                                       ______________________________________                                        EFFECT OF ACID-GRAFTED PHENOXY ON VISCOSITY                                   OF IRON OXIDE-CONTAINING SYSTEMS                                                                   PARTS                                                    ______________________________________                                        Phenoxy PKHH in dimethyl Carbitol                                                                      100                                                  (20% solids)                                                                  20% trimellitic anhydride-Graft                                                                      --        100                                          Phenoxy PKHH (20% solids)                                                     Pferrox 2228 Magnetic Iron Oxide                                                                        42      42                                          Brookfield Viscosity (cps)                                                    (Model RVF, Spindle 4, 25.5° C.)                                       2 rpm                  29,000  10,000                                         20 rpm                  7,600   3,800                                         2/20 ratio             3.8     2.6                                            When the compositions shown in Table VII                                      were reproduced, but replacing dimethyl carbitol                              with a like amount of cyclohexanone, the viscosity                            results were as follows:                                                      2 rpm                  44,000  22,000                                         20 rpm                 13,400   9,800                                         2/20 ratio             3.3     2.2                                            ______________________________________                                    

I claim:
 1. A magnetic coating composition for magnetic recording mediacomprising:(a) a phenoxy resin having pendant secondary hydroxyl groupsof which about 3 to about 50% of such hydroxyl groups have been reactedto produce moieties having pendant carboxyl groups, (b) a magneticpowder, and (c) an organic solvent.
 2. A composition of claim 1 whereinthe magnetic powder is present in the concentration range of about 1:1to about 30:1 magnetic power:phenoxy resin.
 3. A composition of claim 2wherein the magnetic powder is present in the concentration range ofabout 1.5:1 to about 10:1 magnetic powder:phenoxy resin.
 4. Acomposition of claim 1 wherein about 5 to about 25% of said hydroxylgroups have been so reacted.
 5. A composition of claim 1 wherein themagnetic powder is iron oxide.
 6. A composition of claim 1 wherein thehydroxyl groups have been reacted with a monoanhydride to produce thecarboxyl groups.
 7. A composition of claim 6 wherein the monoanhydrideis succinic anhydride.
 8. A composition of claim 6 wherein themonoanhydride is trimellitic anhydride.
 9. A composition of claim 1wherein the phenoxy resin is Phenoxy PKHH.
 10. A composition of claim 1wherein the organic solvent is dimethyl Carbitol.
 11. A composition ofclaim 1 wherein the organic solvent is cyclohexanone.